This invention relates generally to the field of manufacturing substrates and specifically to methods and apparatus for providing a gas-liquid vapor to a process tank.
In the manufacture of semiconductors, semiconductor devices are produced on thin disk-like objects called wafers. Generally, each wafer contains a plurality of semiconductor devices. In producing semiconductor devices, wafers are subjects to a multitude of processing steps before a viable end product can be produced. These processing steps include: chemical-etching, wafer grinding, photoresist stripping, masking, cleaning, rinsing, and drying. Many of these steps require that the wafer be subjected to one or more chemicals. These steps typically occur in a process tank. The chemicals used to process the wafers come in a variety of phases and combinations, including: liquid, gas, liquid-liquid mixtures; gas dissolved in a liquid; and gas-liquid vapors.
A particularly important process step in the wafer manufacturing process is the drying step. A such, a multitude of methods and apparatus exist for use in this process. In order to dry wafers after cleaning, many of these methods and apparatus apply Marangoni-style techniques. In utilizing, Marangoni-style drying techniques, the surfaces of the wafers are exposed to a gas-liquid vapor comprising nitrogen (N2) and isopropyl alcohol (IPA). This typically occurs by blowing the N2-IPA vapor over the wafer surfaces. Exposing the surfaces of the wafers to the N2-IPA vapor speeds up the evaporation of any liquids left on the wafer surfaces. As such, enhanced drying occurs at a faster rate. However, because drying typically occurs after cleaning the wafers, it is imperative that the wafers not be contaminated during the drying process. Additionally, because the rate of drying is related to the concentration ratio of IPA and N2 in the N2-IPA vapor, it is important that this ratio be controlled during the drying process.
Current systems, apparatus, and methods fail to achieve these objectives. In existing systems, the N2-IPA vapor that is used to dry the wafers is created by bubbling N2 into a liquid bath of IPA. The N2 then escapes from the IPA bath carrying IPA vapor with it. This N2-IPA vapor is then transported to the process tank to the dry the wafers. However, it is often the case that the IPA liquid contains contaminants. Thus, because the N2 gas comes into direct contact with the IPA liquid, some of these contaminants will be carried with the N2-IPA vapor and subsequently contact the wafer surfaces. As such, the wafers become contaminated after cleaning, resulting in failed devices and lower yields.
An additional problem of current drying systems using N2-IPA vapor is that there is currently no way to control the concentration ratio of N2 and IPA in the N2-IPA vapor as it enters the process tank. If the N2-IPA vapor is not fully saturated with IPA, a less than optimal cleaning effect will result. Prior art methods and apparatus rely on the fact that the N2 gas will become fully saturated as it passe through the liquid IPA. However, because the saturation method is unpredictable and ineffective, this is not always the case. As such, the wafers can be left “wet” or drying time will be increased. Leaving the wafers “wet” will cause devices fail. Moreover, if a lesser level of IPA is needed in the N2-IPA vapor than that which is being supplied to dry the wafers, IPA is being wasted. Thus, a need exists to be able to control the level of IPA in the N2-IPA vapor.